Polymer additives, such as nucleating agents and clarifying agents, are used to modify the properties (e.g., physical properties) of polymers, such as thermoplastic polymers. For example, clarifying agents are used to reduce the haze of polypropylene by reducing the size of spherulites within the polymer. Also, nucleating agents are used to change the temperature and/or rate at which a polymer crystallizes as it cools from a molten state.
Polymer additives are typically sold by the manufacturer in the form of a powder. Under certain circumstances, these powders can be difficult to handle. For example, powdered polymer additives can unevenly flow from a vessel, such as a hopper from which the additive is dispensed during polymer processing. The uneven flow may be the result of “ratholing,” in which voids or tunnels form in the powder, or “bridging,” in which the powder forms structures that obstruct the flow within the vessel.
In order to address the difficulties associated with the handling of powdered polymer additives, some manufacturers and additive suppliers have begun to produce “no dust blends” or “non-dusting blends,” which are pelletized blends of several polymer additives, such as antioxidants, acid scavengers, light stabilizers, and nucleating agents. These “no dust blends” or “non-dusting blends” may contain a binder to provide structure and stability to the individual pellets. While these “no dust blends” or “non-dusting blends” do exhibit improved flow properties relative to the powdered polymer additives, the relatively hard nature of the individual pellets may not allow certain polymer additives to fully disperse within the polymer to which the pellet is added. These dispersion problems can become more pronounced as the concentration of the polymer additive (e.g., clarifying agent or nucleating agent) increases. Further, the process used to make these “no dust blends” or “non-dusting blends” adds cost to the polyolefin production process.
A need therefore remains for compositions containing polymer additives that exhibit improved flow properties without deleteriously affecting the performance of the polymer additive. The compositions and methods described herein are believed to address this need.